Hypothalamic representation of aggressiveness across mouse strains

Aggression is an innate behavior conserved across species, serving as a critical means to compete for food, mating opportunities, and other essential resources. A central question in aggression research is the extent to which inter-individual variability in aggression is shaped by genetic factors. Here, we examine aggressive behaviors in naïve male mice across seven genetically defined strains and find large cross-strain differences. We find a tight correlation between aggressiveness and anxiety levels across strains, but not within the same strain, suggesting strong genetic control of both traits. Pharmacologically elevating anxiety in high-aggression strains reduces aggression, revealing a causal relationship between these behaviors. We further demonstrate that differences in the synaptic and cellular properties of neurons in the ventrolateral ventromedial hypothalamus (VMHvl) largely account for cross-strain variability in male aggression, and that chemogenetically increasing VMHvl excitability enhances attack behavior in a low-aggression strain. Together, these findings reveal the neuronal implementation of the genetic control of innate aggression level. Genetics profoundly influences aggression by shaping neural circuits, but the underlying mechanisms remain unclear. Here, authors show that strain differences in male mouse aggression are linked to differences in VMHvl neuron physiology.